1. Field of Invention
The present invention relates to a positive displacement pump to move fluid by changing the volume inside a pump chamber by, for example, a piston or a diaphragm. More particularly, the invention relates to a highly reliable pump having a high flow rate.
2. Description of Related Art
Such a related art pump of this type generally has a structure that includes a check valve mounted between an inlet flow path and a pump chamber whose volume can be changed and between an outlet flow path and the pump chamber, as disclosed in Japanese Unexamined Patent Application Publication No. 10-220357 (JP 357).
The related art also includes a pump structure to cause fluid to flow in one direction by making use of viscosity resistance of the fluid. This structure includes a valve at an outlet flow path. In this structure, fluid resistance at an inlet flow path is greater than at the outlet flow path when the valve is opened, as disclosed in Japanese Unexamined Patent Application Publication No. 08-312537 (JP 537).
The related art also includes a pump structure which makes it possible to increase reliability of a pump without using a movable part for a valve. This structure includes a compressive structural device having an inlet flow path and an outlet flow path with shapes in which a pressure drop differs depending on the direction of fluid flow, as disclosed in Published Japanese Translation of PCT International Publication for Patent Application No. 08-506874 of (JP 874), and Anders Olsson, “An Improved Valve-Less Pump Fabricate Using Deep Reactive Ion Etching,” 1996, IEEE 9th International Workshop on Microelectromechanical Systems, pp. 479 to 484 (Olsson).